1. Field of the Invention
This invention relates to the field of repeatable runout cancellation, and more particularly relates to repeatable runout cancellation systems in disk drives.
2. Description of the Related Art
Many systems have repeatable runout (RRO) signals that need to be cancelled to prevent errors. RRO signals are predictable because of their periodic nature. RRO signals have many origins. In disk drives, imperfections in a disk assembly or the data storage media, misaligned or unbalanced disk platters, a tilt in the spindle motor, or eccentricities introduced into data tracks at servo write time may cause RRO signals. These or other defects may cause synchronized harmonic disturbances when the disk rotates. These defects are not related to track density, and therefore do not scale with the track density. This means that as track densities increase in modem disk drives, the RRO signals have more negative effects on the disk drive's ability to properly read and write data from the disk. Methods that have been used in the past to cancel RRO signals are no longer fast enough or complete enough for modem track densities. These methods cancel only the sinusoidal components of the RRO signals, while leaving the non-sinusoidal RRO signals.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method to remove both sinusoidal and non-sinusoidal RRO components from an input signal. Beneficially, such an apparatus, system, and method would react quickly to disturbances, without instability from overcorrecting.